Figure 2. The mean score of imagery valence rating. Error bars represent
the standard error. The asterisks indicate significant differences among
conditions
(**p <.01,
*p <.05).
3.2. ERP results
Repeated-measures ANOVA analysis of LPP amplitudes revealed a
significant interaction between group and emotion
(F (2, 164)=13.40,p <0.001,ηp2 =0.14). Simple effects
analyses showed that depressed participants exhibited larger LPP for sad
imagery compared to happy imagery (p =0.008); no significant
differences were found for sad (p =0.05) and happy imagery
(p =1.00) compared to neutral imagery. Conversely, healthy
controls exhibited greater LPP for happy imagery than for sad imagery
(p <0.001); no significant differences were found for
happy(p =0.08) and sad imagery(p= 0.17) compared to neutral
imagery. Additionally, depressed individuals exhibited significantly
larger LPP for sad imagery compared to healthy controls( p =0.03).
The main effect of the time window was significant (F (2,
164)=14.05, p <0.001,ηp2 =0.15), and wherein the LPP
amplitudes were more positive in the early (p =0.003) and middle
(p <0.001) time
windows compared to the late time window. The main effects of group and
emotion, as well as the interaction effects of group and time window,
emotion and time window, were not significant (ps >
0.23).
The interaction effect of group × emotion × time window was significant
(F (4, 328)=14.05, p =0.03,ηp2 =0.03), followed up by
separate analyses of the three time windows.
Early LPP amplitudes. The results showed a significant
interaction effect between group and emotion (F (2, 164) =11.07,p <0.001,ηp2 =0.12). Simple effect
analysis showed that depressed participants exhibited significantly
larger early LPP for sad imagery compared to both happy ( p =0.03)
and neutral imagery ( p =0.02). Conversely, healthy controls
exhibited greater early LPP for happy imagery than for sad imagery
(p =0.001), and greater but non-significant than neutral imagery
(p =0.18).
No other effects reached
significance (ps >0.39).
Middle LPP amplitudes. The results revealed a significant
interaction effect between group and emotion (F (2, 164)=12.40,p <0.001,ηp2 =0.13). Simple effect
analysis showed that depressed participants exhibited significantly
larger middle LPP for sad imagery compared to both happy
(p =0.003) and neutral imagery
(p =0.02). Conversely,
healthy controls exhibited greater middle LPP for happy imagery compared
to sad imagery (p =0.003), and
greater but non-significant than
neutral imagery( p =0.07). Additionally, depressed individuals
exhibited larger middle LPP for sad imagery relative to healthy controls
(p =0.02). No other effects reached significance
(ps >0.29).
Late LPP amplitudes. The results revealed a significant
interaction effect between group and emotion (F (2, 164)=10.73,p <0.001,ηp2 =0.12). Simple effect
analysis showed that depressed participants exhibited significantly
larger late LPP for sad imagery compared to happy imagery
(p =0.04), but no significant difference was observed between late
LPP for happy imagery and neutral imagery (p =0.56). For the
control group, happy imagery elicited greater late LPP than sad imagery
(p =0.001), and greater but non-significant than neutral imagery
(p =0.17). Furthermore, the depression group exhibited
significantly larger late LPP for sad imagery compared to the control
group (p =0.02). No other effects reached significance (ps >0.45). See Figure 3 and Figure 4.